Ventricular Arrhythmias in Heart Failure: To Treat or not to Treat?

Ventricular electrophysiology in congestive heart failure and its correlation with heart rate variability and baroreflex sensitivity: a canine model study

AIMS

This study investigated ventricular electrophysiological characteristics and the correlation between these parameters and heart rate variability (HRV) and baroreflex sensitivity (BRS) in a canine congestive heart failure (CHF) model.

METHODS AND RESULTS

Haemodynamics, HRV, BRS, and ventricular electrophysiological variables were measured 4-5 weeks after sham operation (control dogs) and pacemaker implantation, and rapid right ventricular pacing at 240 bpm (CHF group). In the CHF group, significant differences from the control group in ventricular effective refractory period (VERP), monophasic action potential (MAP) duration (MAPD(90)), ventricular late repolarization duration (VLRD), the ratio of VERP to MAPD(90), dispersion of ventricular recovery time (VRT-D), and ventricular fibrillation threshold (VFT) were noted. Both BRS and the time and power domain parameters of HRV were significantly decreased in the CHF group compared with the control group, and a significant, positive correlation between HRV and BRS was identified in the CHF group. Heart rate variability and BRS were negatively and significantly correlated with VLRD and VRT-D, and were positively correlated with VERP/MAPD(90) and VFT in the CHF group.

CONCLUSION

These results suggest that ventricular electrophysiological characteristics correlated with abnormal autonomic nerve function may have important effects on sudden cardiac death. Further research is warranted.

Sudden cardiac death syndrome and pump dysfunction: the link

Clearly, sudden cardiac death syndrome in heart failure is linked to severely perturbed neurohumoral, hemodynamic, and mechanical systems. Routine antiarrhythmic drug therapy has not proven beneficial and, therefore, there is no justification for using these agents in unselected heart failure patients who are without significant symptomatic ventricular arrhythmia. Aggressive treatment of the failure syndrome seems most important. Because many of the problematic arrhythmias arise from triggering automaticity, which is known to occur in excessive ventricular stretch and wall stress, systemic vascular "unloading" with vasodilators and angiotensin-converting enzyme inhibitors is likely helpful. The most recent American College of Cardiology/American Heart Association Guidelines regarding therapeutic management of heart failure suggest that aggressive pharmacologic treatment of asymptomatic ventricular arrhythmias is best avoided. To be considered strongly for pharmacologic prescription or for implantation of a tachyarrhythmia termination device, a patient should have symptomatic ventricular tachycardia with an episode of syncope or sudden cardiac death syndrome rather than simply having palpitations of asymptomatic, unsustained ventricular tachycardia. Indeed, aggressively treating congestive heart failure with medication often eliminates potentially life-threatening arrhythmias. Appropriate use of vasodilators and, particularly, angiotensin-converting enzyme inhibitors is important. Correction of fluid balance and electrolyte disorders may be helpful to address symptoms and certainly is likely to decrease the potential for morbidity and mortality. On occasion it may be necessary to consider bradyarrhythmia pacemaker insertion or the use of atrioventricular nodal-ablation techniques with subsequent ventricular or atrioventricular pacer insertion. Obviously, sudden cardiac death due to sudden heart block or asystole might be attenuated with this strategy.

Neural control of left ventricular contractility in the dog heart: synaptic interactions of negative inotropic vagal preganglionic neurons in the nucleus ambiguus with tyrosine hydroxylase immunoreactive terminals

Recent physiological evidence indicates that vagal postganglionic control of left ventricular contractility is mediated by neurons found in a ventricular epicardial fat pad ganglion. In the dog this region has been referred to as the cranial medial ventricular (CMV) ganglion [J.L. Ardell, Structure and function of mammalian intrinsic cardiac neurons, in: J.A. Armour, J.L. Ardell (Eds.). Neurocardiology, Oxford Univ. Press, New York, 1994, pp. 95-114; B.X. Yuan, J.L. Ardell, D.A. Hopkins, A.M. Losier, J.A. Armour, Gross and microscopic anatomy of the canine intrinsic cardiac nervous system, Anat. Rec., 239 (1994) 75-87]. Since activation of the vagal neuronal input to the CMV ganglion reduces left ventricular contractility without influencing cardiac rate or AV conduction, this ganglion contains a functionally selective pool of negative inotropic parasympathetic postganglionic neurons. In the present report we have defined the light microscopic distribution of preganglionic negative inotropic neurons in the CNS which are retrogradely labeled from the CMV ganglion. Some tissues were also processed for the simultaneous immunocytochemical visualization of tyrosine hydroxylase (TH: a marker for catecholaminergic neurons) and examined with both light microscopic and electron microscopic methods. Histochemically visualized neurons were observed in a long slender column in the ventrolateral nucleus ambiguus (NA-VL). The greatest number of retrogradely labeled neurons were observed just rostral to the level of the area postrema. TH perikarya and dendrites were commonly observed interspersed with vagal motoneurons in the NA-VL. TH nerve terminals formed axo-dendritic synapses upon negative inotropic vagal motoneurons, however the origin of these terminals remains to be determined. We conclude that synaptic interactions exist which would permit the parasympathetic preganglionic vagal control of left ventricular contractility to be modulated monosynaptically by catecholaminergic afferents to the NA-VL.

Suppressing sympathetic activation with clonidine on ventricular arrhythmias in congestive heart failure

This randomized, double-blind, placebo-controlled study examines the effects of clonidine (a centrally acting sympathoinhibitor) on ventricular arrhythmias in 35 patients with congestive heart failure (CHF) by using the 24-h ambulatory electrocardiographic recording. After baseline examination and Holter recording, patients were balanced and 18 patients were randomized to clonidine group and 17 patients to placebo group. After four weeks of clonidine (given as a transdermal patch) or matching placebo therapy, a second Holter recording was obtained. The placebo group showed no change in the frequency of ventricular arrhythmias whereas the clonidine-treated group showed a significant decrease in the frequency of ventricular premature beats by 68% (P<0.01), couplets by 63% (P<0.01) and episodes of non-sustained ventricular tachycardia by 60% (P<0.05). Clonidine also decreased heart rate and arterial blood pressure, but left ventricular ejection fraction was slightly improved. It is concluded that sympathetic suppression with clonidine reduces the frequency of ventricular arrhythmias in patients with CHF, which suggests that sympathetic activation plays a role in arrhythmogenesis in these patients.

Mechanisms and management of ventricular dysrhythmias in heart failure

Despite recent pharmacologic and surgical advances in the management of heart failure, the morbidity and mortality rates of this chronic illness remain high. Ventricular dysrhythmias are common in heart failure and may be independently associated with increased mortality rates. Although the risks of sudden cardiac death leading to the patient's death are increased by the presence of complex ventricular dysrhythmias, the management of dysrhythmias is subject to controversy. The purpose of this article is to review the normal electrophysiologic properties of the heart and to examine the likely mechanisms, diagnostic approaches, and proposed treatments for ventricular dysrhythmias in heart failure.

Depressed arterial baroreflex sensitivity and not reduced heart rate variability identifies patients with chronic heart failure and nonsustained ventricular tachycardia: the effect of high ventricular filling pressure

In chronic heart failure (CHF) the contributing role of increased sympathetic activity and hemodynamic dysfunction in the genesis of ventricular arrhythmias has not been well established. To assess the relation between severe ventricular arrhythmias, hemodynamic impairment, and autonomic nervous system derangement, 142 patients with CHF in sinus rhythm underwent 24-hour electrocardiographic recording, right-sided heart catheterization, and evaluation of sympathovagal balance by heart rate variability (HRV) and baroreflex sensitivity (BRS). Patients were grouped according to the absence (without nonsustained ventricular tachycardia [NSVT]; n = 87) or presence (with NSVT; n = 55) of NSVT. Patients with NSVT had higher pulmonary artery and capillary pressures and more pronounced signs of sympathetic activation and parasympathetic withdrawal compared with those without NSVT. However, logistic regression analysis revealed that depressed BRS but not reduced HRV was significantly associated with the presence of NSVT, at both univariate analysis and after adjustment for clinical and hemodynamic variables. Moreover, it was found that when depressed BRS was associated with high pulmonary capillary pressure, the odds ratio for having NSVT rose markedly from 3.8 to 6.5. In conclusion, this study indicates that in stable CHF the assessment of arterial baroreflex function, but not HRV analysis, allows identification of patients at high risk of NSVT. It is suggested that the effect of depressed BRS is strengthened by the simultaneous presence of increased myocardial wall stress. These data support the hypothesis of a contributory role of autonomic nervous system dysfunction as expressed by the inability to activate effective vagal reflexes and an indirect index of ventricular stretch in the genesis of life-threatening arrhythmias.

Selection and treatment of candidates for heart transplantation. A statement for health professionals from the Committee on Heart Failure and Cardiac Transplantation of the Council on Clinical Cardiology, American Heart Association

Improved outcome of heart failure in response to medical therapy, coupled with a critical shortage of donor organs, makes it imperative to restrict heart transplantation to patients who are most disabled by heart failure and who are likely to derive the maximum benefit from transplantation. Hemodynamic and functional indexes of prognosis are helpful in identifying these patients. Stratification of ambulatory heart failure patients by objective criteria, such as peak exercise oxygen consumption, has improved ability to select appropriate adult patients for heart transplantation. Such patients will have a poor prognosis despite optimal medical therapy. When determining the impact of individual comorbid conditions on a patient's candidacy for heart transplantation, the detrimental effects of each condition on posttransplantation outcome should be weighed. Evaluation of patients with severe heart failure should be done by a multidisciplinary team that is expert in management of heart failure, performance of cardiac surgery in patients with low left ventricular ejection fraction, and transplantation. Potential heart transplant candidates should be reevaluated on a regular basis to assess continued need for transplantation. Long-term management of heart failure should include continuity of care by an experienced physician, optimal dosing in conventional therapy, and periodic reevaluation of left ventricular function and exercise capacity. The outcome of high-risk conventional cardiovascular surgery should be weighed against that of transplantation in patients with ischemic and valvular heart disease. Establishment of regional specialized heart failure centers may improve access to optimal medical therapy and new promising medical and surgical treatments for these patients as well as stimulate investigative efforts to accelerate progress in this critical area.